1. Technical Field
The invention relates generally to nitride-based semiconductor structures, and more particularly to an inverted nitride-based semiconductor structure in which the active layer comprises Indium.
2. Background Art
To date, a typical nitride-based semiconductor, such as a modulation-doped field effect transistor (FET) and the like, has a “normal” metal-AlGaN-GaN structure. In this case, the AlGaN layer is deposited on top of an undoped GaN layer, and the device channel is in the GaN layer at the AlGaN-GaN heterointerface. As a result, the distance between the two-dimensional (2-D) electron gas in the device channel and the metal is equal to the thickness of the AlGaN layer plus the effective thickness of the device channel.
For various types of semiconductor structures, such as an arsenic-based heterostructure FET, a higher transconductance can be obtained by inverting an AlGaAs-GaAs heterostructure. In this case, the “normal” metal-AlGaAs-GaAs structure is altered to metal-GaAs-AlGaAs, while the device channel is formed in the GaAs layer at the AlGaAs-GaAs heterointerface. To this extent, the distance between the 2-D electron gas in the device channel and the metal is equal to the thickness of the GaAs layer minus the effective thickness of the device channel. As a result, for a comparable structure, the 2-D electron gas is closer to the gate than in the normal structure thereby providing a higher transconductance.
Due to a high breakdown field, nitride-based semiconductor devices are desirable over other types of devices (e.g., arsenic-based semiconductor devices) for applications that require high voltage, high power, and the like. Additionally, other improvements, such as the inclusion of two field plates, can be implemented to significantly improve the breakdown voltage in Reduced Surface Field (RESURF) devices. To provide for a higher transconductance in nitride-based semiconductor structures, an AlGaN-GaN inverted structure has been developed, and a nitride-based FET has been developed which includes an AlGaN-GaN heterojunction with the inverted 2-D channel. However, this device exhibited operational characteristics that were not superior to those of a normal AlGaN-GaN heterostructure FET. In particular, since the device required a conventional buffer layer to avoid a dislocation formation, the quality of the materials was insufficient to demonstrate an improved performance.
As a result, a need exists for an improved nitride-based semiconductor structure in which an inverted channel design can be effectively incorporated to achieve a higher transconductance for a resulting device. The structure can be used to create a device, such as a FET, having improved performance characteristics.